Skeletal muscles are composed of fibres having different morphological,
contractile and metabolic characteristics. The number of
muscle fibres is fixed at birth (Wigmore & Stickland, 1983). Muscle
size can also increase by satellite cell proliferation which isconsidered unimportant. Therefore, muscle growth and ultimate
muscle mass are largely determined by the initial number of muscle
fibres, the growth of the cross-sectional area and the length of
individual muscle fibres. If the number of fibres in a muscle is low
compared to the high number of muscle fibres, the thickness of
muscle fibres must increase more in order to attain the same muscle
mass at slaughter.